1. Field of the Invention
The present invention relates to a method of operating a power-station plant according to the preamble of claims 1 and 2.
2. Discussion of Background
In a power station plant which comprises a gasturbine group, a waste-heat steam generator arranged downstream, and an adjoining steam circuit, it is advantageous to provide a supercritical steam process in the steam circuit in order to achieve a maximum efficiency.
CH-480 535 has disclosed such a circuit. In this circuit, for the purpose of optimum utilization of the waste heat of the gas-turbine group in the lower temperature range of the waste-heat steam generator, a mass flow of the circuit medium of the gas turbine is branched off and utilized recuperatively in the gas turbine. Both the gas-turbine process and the steam process have sequential combustion. However, in the case of modern gas turbines preferably of single-shaft design, this configuration leads to an undesirable complication with regard to construction.
In a plant which has been disclosed and is equipped with an intercooler in operative connection with the compressor unit, a large portion, or even the entire quantity, of the accumulating hot water is directed out of this intercooler into a mixing preheater belonging to the steam circuit. With this measure, excess heat, which causes some of the water to evaporate, develops in the mixing preheater. The steam which is thus produced can then be fed via a line holding the vacuum to a steam turbine in which work is performed. However, such an arrangement has the disadvantage that the large-volume flow path of the low-pressure part of the steam turbine has to be enlarged even further. The work gain of this steam quantity is relatively small; at most it could just be sufficient to compensate for the adverse effect of the intercooler on the efficiency of the power station plant.